1. Field of the Invention
This invention relates to a pressurized hot air pipe of an aircraft that is equipped with a leak detection device as well as a segment of said pipe.
2. Description of the Related Art
At 10, FIG. 1 shows an aircraft that integrates different sources of pressurized air that are connected, by a pipe network 12, to systems that have pressurized air requirements.
The engines 14 as well as the auxiliary power group 16 constitute pressurized hot-air sources that are integrated into the aircraft. The latter can also comprise means 18 for connecting an externally pressurized air source, whereby said means 18 are located under the aircraft for supplying it with pressurized air when it is on the ground.
As a system that uses pressurized air, the aircraft comprises, i.a., air-conditioning systems 20, wing-defrosting systems 22, ventilation systems, engine-starting systems, and the fuel-tank pressurization system.
FIGS. 2 and 3 show a portion of a pipe that makes it possible to channel the pressurized air from a source up to a system that uses it. This pipe consists of segments 24 placed end to end. Each segment 24 comprises an inner tube 26, an outer tube 28 that is essentially coaxial to the first, and heat-insulating material 30 that is inserted between the tubes 26 and 28.
According to one embodiment, the inner tube 26 is obtained from one or more flat panels, made in particular of titanium, shaped, and then welded on one or more generatrices 32. The inner tubes 26 comprise collars 34 at each end.
The insulating material 30 can be based on glass wool.
The outer tube 28 comes in the form of a sheet, made in particular of titanium, connected to the insulating material.
To ensure the connection between two adjacent segments placed end to end, a clamp 36 is used that clamps the collars 34.
Each junction zone is insulated by connecting a sleeve 38, astride two segments, with the ends of the sleeve 38 clamping the outer tubes 28 in such a way as to produce an essentially airtight connection between the outer tubes 28 and the sleeve 38. Thus, the sleeve 38 and the ends of the inner tubes 26 border an annular chamber 40.
According to one embodiment, the wall of the sleeve is flexible and comprises an insulating material that is bagged between two films made of plastic material.
Advantageously, a pipe that channels pressurized hot air comprises a leak detection device that makes it possible to indicate the presence of an air leak, advantageously its location, so as to warn of risks of damage to the structure of the aircraft or elements that are present in the environment of this possible leak because of the high temperature of the pressurized air.
This detection device comprises at least one long-member detection element A that consists of heat-sensitive sensors, connected in series, arranged outside of the outer tubes 28.
The long-member detection element A is semi-rigid and can be twisted so as to adapt its shape to the desired detection path.
According to one embodiment, the sensors have a resistance that varies based on temperature. In the absence of a leak, the potential that is measured at a first end of the loop is identical to the potential that is measured at the other end. In the presence of a leak, the potentials are different.
The positioning of the leak can be determined based on the ratio between the two potentials. Thus, V1/V2=y/x, with V1 being the potential measured at the first end, V2 the potential measured at the second end, x the distance separating the leak from the first end, and y the distance separating the leak from the second end.
Advantageously, the detection system comprises two detection elements A and B that are parallel and face in opposite directions so as to be able to easily locate the leak.
For optimal operation, the detection elements A and B are arranged at a certain distance from the outer tube 28. Consequently, these detection elements A and B are connected to the tube by braces 42 that are distributed along the path of the detection elements A and B that suitably position the detection element(s) relative to the outer tube 28. According to one embodiment, each brace 42 comprises a sleeve into which the detection element passes and a base that is attached to the outside surface of the outer tube 28. Taking into account the embodiment of the pipe, the zones where the leaks can potentially appear are essentially junction zones between the segments and optionally along the weld beads of the generatrix or generatrices 32 of the inner tube 26.
To detect a leak at the generatrix or generatrices 32, the outer tube comprises openings 44 or groups of small openings close to the generatrix or generatrices 32, and the detection elements are arranged outside of the outer tube perpendicular to the openings 44.
To detect a leak at junction zones, each sleeve 38 comprises at least one opening 46. In the case of a leak at the connection between two segments, pressurized hot air escapes into the annular chamber 40 and then via the opening 46. Regardless of the angular position of the leak at the junction, the opening 46 makes it possible to channel the hot air in the direction of the detection element(s).
So that this leak is detected, it is necessary that a portion of the detection element or a portion of each detection element passes above the opening 46. Close to each opening 46, the braces 42 that are used to hold the detection element(s) A and B are arranged outside of the zones covered by the sleeve 38 so as not to perforate it, although they are relatively distant from the opening 46.
This arrangement of the detection device cannot be completely satisfactory for the following reasons:
According to a first drawback, a brace 42 can be arranged at the openings 44 and may obstruct them, which tends to reduce the capacities of the detection element to detect a leak that can appear at these openings. According to another drawback, it may prove difficult to arrange the detection element(s) A and B correctly relative to the opening 46. On the one hand, it is difficult to preserve the alignment between the detection element A or B and the openings 46. If the detection element A or B is not aligned, it is possible to correct this poor alignment by deforming the detection element A or B in such a way that a portion is arranged facing the opening 46. However, taking into account how far away the braces 42 are, the path followed by the detection element may be accidentally modified and may no longer pass facing the opening 46.
On the other hand, to ensure an optimal operation of the leak detection system, it is necessary that the detection elements be arranged at an optimal distance from the opening 46. To correct this spacing, it is possible to deform the detection element A or B in such a way that the distance separating it from the opening is optimal. However, as above, taking into account how far away the braces 42 are, the path taken by the detection element may be accidentally modified and the spacing between the loop and the opening 46 may no longer be optimal.
According to a last drawback, in certain situations, it may not be possible to provide an opening 46 at the sleeve 38, in particular if the surrounding elements are heat-sensitive. In this case, it is not possible to detect a possible leak at the junction that is covered by a sleeve without an opening 46.